Senile plaques

Senile plaques (also known as neuritic plaques) are extracellular deposits of amyloid beta in the grey matter of the brain. Degenerative neural structures and an abundance of microglia and astrocytes can be associated with senile plaque deposits. These deposits can also be a byproduct of senescence (ageing). However, large numbers of senile plaques and neurofibrillary tangles are characteristic features of Alzheimer's disease. Abnormal neurites in senile plaques are composed primarily of paired helical filaments, a component of neurofibrillary tangles. The plaques are variable in shape and size, but are on average 50 µm in size. In Alzheimer's disease they are primarily composed of amyloid beta peptides. These polypeptides tend to aggregate and are believed to be neurotoxic.